A specific allele of the T/t locus in the house mouse, tw32, is known to cause abnormalities in sperm metabolism and sperm surface components. Recent evidence from our laboratory suggests that this same allele somehow advances the time of sperm penetration and pronuclear appearance in the egg. We want to learn how the known abnormalities of these spermatozoa can influence the timing of events in fertilization. We propose to use spermatozoa from congenic strains of mice, differing only with respect to the T/t locus and closely linked genes, to investigate the effect of tw32 on sperm penetration of the egg investments. Studies will be made of the effect on the timing of sperm penetration in vitro of sequential removal of the cumulus and zonae pellucida, of the 3-dimensional distribution of spermatozoa in the egg investments after insemination in vivo, and of fluorescently-labelled and unlabelled spermatozoa competing for penetration of a single set of eggs and their investments. Since motility may also be important for sperm penetration of egg investments, several components of sperm motility will also be studied. We also propose to study the timing of sperm penetration and appearance of pronuclei in vitro, by means of light and electron microscope observations. Consistent differences from the congenic controls in the timing or morphology of events in fertilization could suggest a role for the abnormal sperm components in specific mechanisms important for fertilization. A better understanding of the sperm's function in fertilization will provide insight into the processes involved in mammalian fertilization. It may also suggest new approaches to the management of human fertilization, either to correct defects, or to prevent conception.